1. Field of the Invention
The present invention relates to a radiation structure without a light guiding board, especially to a radiating surface that achieves an even scattering from a diffusion plate even if the guiding board is not used in a backlight module or the like.
2. Description of the Related Art
A conventional backlight module for a liquid crystal display disclosed in Taiwan patent published number 200825553, “A BACKLIGHT MODULE”. The referred backlight module comprises at least one light guiding board, at least one light source disposed at one side of the light guiding board, a diffusion plate mounted above the guiding board, not contacting the guiding board, and a mixing cavity defined between the light guiding board and the diffusion plate. Whereby, the streams of light emitted from an emission plane of the light guiding board would be adequately mixed in the mixing cavity, thence allowing the light to be emitted via the diffusion plate toward the backlight module. However, such conventional backlight module includes the following shortcomings:
The design of the backlight module mostly employs the light guiding board to serve as a guiding medium of the light source. Nonetheless, after the light source passing through the light guiding board, certain consumption of energy would lower the emitting efficiency. Especially, in view of the consumption, most side-edged backlight modules in a medium size could merely provide the emitting efficiency less than 70%, and the backlight module adapted to monitors even adversely provides the emitting efficiency just a bit higher than 50%.
“Planar light source device and display device using the same device” issued by a U.S. Pat. No. 7,350,951 reforms the structure of the optical reflector at the bottom thereof to obtain a radiation structure without a light guiding board. Whereby, the emitting efficiency of the light could be increased. However, shortcomings still exist in such disclosure:
Although the optical reflector at the bottom utilizes a raised middle portion to promote the illumination refracted from the diffusion plate, such structure readily has the optical reflector reflect or scatter an uneven luminosity. Namely, the emission plane generated from the refraction of the diffusion plate has an uneven illumination. Additionally, if no optical element is employed to guide the projection of the streams of light, the occurrence of the brighter two sides with a darker middle section would be adversely resulted.